Cybermen are neither evil nor good, just clinically logical in their actions: they have no concept of fear, pity, joy or cruelty, owing to their scientific advances. The once human Inhabitants of their home planet, Mondas, developed the science of cybernetics to the extent that they could replace every part of the human body, exept the brain, with metal or plastic parts. They became Cybermen, silver humanoid giants that are immune to extremes of heat and cold and free from the ravages of disease. Eventually, their scientists eliminated what they saw as imperfections in their brains: emotions, without which they have become creatures of pure logic.
Human bodies, however, are essential to the survival of the Cybermen, because the Cyberman can increase their numbers only by converting suitable subjects. It is the object of propagating the Cybermen race that drives them to travel through space. Earth and its colonies are therefore often chosen as targets of Cybermen attacks; it was during such an attack on Earth in 1986 that the Doctor destroyed Mondas, which had returned to its home solar system. Captured humans are cyberized, a process of physical replacement and mental conditioning, in order to become Cybermen; those that reject the conditioning are often used as workers or infiltrated as super-human spies into target societies. Cybermen have also developed mind-controlling machines used in combination with neurotoxins to enslave weak-willed humans.
The typical Cyberman stands about 7 feet tall and has the strength of ten humans. Cybermen do not need oxygen and can survive in the vacuum of space. Although almost invulnerable to conventional attack, Cybermen do have a weakness. Gold is poisonous to them and gold dust can be used to clog their chest units and termnate their life-support system. Cybermen also need to be recharged periodically to reamin active. Extreme cold forces Cybermen into hibernation. The Tombs of the Cybermen located on their adoptive planet Telos are riddled with special refigeration chambers into which the Cybermen retreat to conserve energy. Whenever a Cybermen invasion force travels through deep space, the bulk of it travel in cryogenic chambers from which they must be awakened.
The Cybermen are led from the planet Telos by their supreme leader, the Controller who is distinguishable by his enlarged cranial dome. The Controller first appeared in the Tombs of the Cybermen on Telos, where he eventually seemed to have been destroyed. However, a Controller (claiming to be the same entity) later masterminded the return of the Cybermen to Telos. The Controller has never been known to leave the planet Telos. In the field Cybermen forces are led by a Cyber Leader. Patrols are lead by a Cyber Lieutenant.
Cyber-technology is highly advanced and the Cybermen have constantly refined and upgraded their weapons and appearance over the centuries and 7 distinctive types, as detailed below, have been encountered.
Cybermen have been known to use small metalic rodent-like creatures called cybermats. Cybermats are about 50 centimeters long and built from flexible metal segments. Cybermen employ these small, semi-intellegent robots to infiltrate enemy bases, where they secretively destroy materials and personel, depriving the base of any materials that might be useful to the Cybermen. Cybermats typically move through the service tunnels and ventilation ducts. A cybermat's main weapon is it's poisonous bite. The most commonly used venom is a powerful neurotoxin which can be used to render the victim unconcious and ready them for Cybermen mind-control conditioning. Cybermats can also emit a weak energy bolt from their visual sensors.